US9178628B2 - Method and apparatus for graphic display of I/Q values of a baseband signal - Google Patents

Method and apparatus for graphic display of I/Q values of a baseband signal Download PDF

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US9178628B2
US9178628B2 US14/455,890 US201414455890A US9178628B2 US 9178628 B2 US9178628 B2 US 9178628B2 US 201414455890 A US201414455890 A US 201414455890A US 9178628 B2 US9178628 B2 US 9178628B2
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values
value
selected subset
subset
display information
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Jochen Kraus
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Rohde and Schwarz GmbH and Co KG
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    • H04B17/0042—
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/20—Monitoring; Testing of receivers
    • H04B17/23—Indication means, e.g. displays, alarms, audible means

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  • the present invention relates to a method and a device for the automatic graphic display of I/Q values of a baseband signal by means of a constellation diagram.
  • a constellation diagram serves for the graphic display of received symbols of a digitally modulated signal.
  • the signals arriving in a receiver are evaluated for this purpose on the basis of preamble information of the signal, wherein the respective modulation type, the bit-depth per symbol, the signal source and other information can be contained in the preamble of the signal.
  • this information is obtained from especially reserved subcarriers, for example, the Transmission Parameter Signaling, abbreviated as TPS in the Digital Video Broadcast standard DVB-T.
  • TPS Transmission Parameter Signaling
  • DVB-T Digital Video Broadcast standard
  • the information is simply specified in a fixed manner for each standard, so that a receiver handles the received digital signals according to this fixed specification.
  • the assigned symbols obtained from the received signal in this manner represent complex numbers in this context.
  • a symbol can thus be displayed as a point in the complex I/Q plane—the constellation diagram.
  • the real part of the symbol is designated as the In-Phase component, abbreviated as I.
  • the imaginary part of the symbol is designated as the Quadrature-Phase component, abbreviated as Q.
  • digital signals are transmitted on a high-frequency carrier by varying the magnitude and the phase of the carrier in such a manner that the carrier adopts one of several specific constellation points in the constellation diagram at every clock transition. Every constellation point codes a given symbol which comprises one or more data bits. In this context, a constellation diagram shows the valid constellations for all permitted symbols. In order to obtain the respective symbol, the precise magnitude and the precise phase of the received signal must be determined for every clock transition.
  • a constellation diagram dependsent upon the modulation method used, a constellation diagram comprises a different number of decision fields.
  • a decision field is an area in the constellation diagram in which one constellation point is disposed in each case.
  • the decision fields are often drawn as a grid in the diagram in order to obtain a visual demarcation of the individual constellation points from one another.
  • a signal transmission can be subject to different disturbances.
  • a symbol can be a preamble frame, a data frame or an end frame.
  • Embodiments of the present invention advantageously address the foregoing requirements and needs, as well as others, by providing an approach for the display of constellation diagrams, in which clear visual organization is enhanced, and wherein such an approach avoids increased computational effort, and improves error analysis.
  • methods for the automatic graphic display of I/Q values of a baseband signal are provided by means of a constellation diagram.
  • the method comprises: selecting a subset of I/Q values from a set of I/Q values of a baseband signal, wherein the non-selected I/Q values of the set form a non-selected subset; calculating a frequency of occurrence of each I/Q value of the selected subset; assigning display information to each I/Q value of the selected subset, wherein the display information at least corresponds to the respective frequency of occurrence; and displaying, on a display device, the set of I/Q values of the baseband signal in a constellation diagram, based at least in part on the display information, wherein the I/Q values of the non-selected subset is displayed in a different manner from the I/Q values of the selected subset.
  • the selection, according to such embodiments, of a subgroup of I/Q values from all I/Q values of the baseband signal allows a reduction of N value groups down to only two value groups, namely a selected subgroup and a non-selected subgroup.
  • N value groups down to only two value groups, namely a selected subgroup and a non-selected subgroup.
  • the display is therefore unambiguous under all circumstances and in all configurations, if the I/Q values of the selected subgroup are always permitted to cover the I/Q values of the non-selected I/Q values. Further, none of the I/Q values of the selected subgroup is concealed or covered.
  • the non-selected subset of I/Q values is displayed independently of their frequency of distribution and/or with a relatively lower resolution.
  • the non-selected subgroup is of subordinate interest, so that a detailed display is not required, thereby strongly reducing the computational effort.
  • the method also has the advantage that only the selected subset of I/Q values needs to be taken into consideration for the calculation of frequencies of occurrence. Accordingly, the computational intensity is reduced, wherein an intensity-related display of the selected I/Q values dependent upon their frequencies of occurrence is retained in full.
  • the method according to such an embodiment is compatible with previous display variants. It can be used with all standards and is not a specially adapted solution. Accordingly, very complex transmission methods can be analyzed very well through a corresponding selection, especially, the coded orthogonal frequency multiplex method, abbreviated as Coded-OFDM, which is used as a basis for a series of transmission standards, for example, audio standards, such as DAB, video standards, such as DVB-T2 or DVB-C2, the mobile-radio standard LTE, or communications standards, such as WLAN or Bluetooth 3.0.
  • Coded-OFDM coded orthogonal frequency multiplex method
  • the display information is a color value, a contrast value and/or a brightness value.
  • the individual I/Q values are displayed with a different color or with different contrasts, for example, dependent upon the frequency of occurrence.
  • This embodiment advantageously ensures that very clearly visually organized constellation diagrams are obtained, allowing the maximum possible evaluations in the constellation diagram as a result of the visual distinctness.
  • a multi-stage subdivision based on threshold values for the respective frequency of occurrence of the I/Q value is advantageous. Color gradations in different colors, for example, green, for rare frequencies of occurrence, yellow for medium frequencies of occurrence and red for high frequencies of occurrence, are particularly suitable in order to achieve good visual distinctness of the individual I/Q symbols.
  • the step of calculating the frequencies of occurrence is implemented by means of a counter.
  • a counter In this context, it is registered in a data buffer how often a specific I/Q value—which preferably displays a pixel in the display—has been received.
  • the counter status is then compared with the threshold value used for the respective frequency of occurrence in order to assign a corresponding display information whenever a threshold value is exceeded.
  • the number of threshold values is adjustable so that a user can specify in which gradations of frequency of occurrence the I/Q value is to be displayed for each constellation point.
  • the individual threshold values for the frequency-of-occurrence values are advantageously adjustable by the user, so that the user can adapt the threshold values, and especially their data volume, to the respective baseband signal to be investigated.
  • the I/Q values of the selected subgroup always cover the I/Q values of the non-selected subgroup, which ensures that the selected I/Q values are displayed in every case and not concealed and/or covered by a non-selected I/Q value.
  • the display information of the I/Q values of the non-selected set of all I/Q values is identical, which has the advantage that all non-selected I/Q values are displayed in an identical manner. Accordingly, the user is provided with an intuitive visualization of which I/Q values have not been selected in the constellation diagram.
  • the step of selection is advantageously implemented by the user.
  • the user is requested to make a user entry, where, especially during the demodulation of a received signal, preamble information is evaluated, thereby providing information about which I/Q values are, in principle, present in the baseband signal.
  • preamble information is evaluated, thereby providing information about which I/Q values are, in principle, present in the baseband signal.
  • the preamble can also contain information about different datastreams transmitted in parallel.
  • the selection need not necessarily be based upon preamble information. For example, if reserved subcarriers are used for the transmission of the selection criteria, the selection should be based on the subcarrier information, especially the “Transmission Parameter Signaling”.
  • the information is predefined according to a standard and can be used directly for the selection.
  • the frequency of occurrence for every selected I/Q value is stored with the respective I/Q value itself.
  • a uniform data record is created, which represents both the I/Q value and also the display information and the frequencies of occurrence, which allows a simple buffer management.
  • the step of selection is implemented on the basis of a specific modulation used for the transmission of the I/Q values and different modulation types are imaged in the constellation diagram.
  • the resulting decision fields are correspondingly small because of the plurality of constellation points through modulations of a relatively high order or use of different modulations, so that disturbances in the signal path and a resulting enlarged signal cloud of a constellation point occurs.
  • a subset of I/Q values of a specific modulation is selected in order to implement an unambiguous assignment of the I/Q values.
  • the selection is implemented on the basis of a specific symbol of the baseband signal. Accordingly, this refers, for example, to specific groups and/or classes of OFDM symbols, which is particularly advantageous if several specific symbols define the same constellation point in the constellation diagram. By way of example, by selecting a specific symbol, I/Q values of only this symbol are displayed, thereby simplifying the error analysis.
  • the selection is implemented on the basis of a specific signal source of the baseband signal.
  • a signal transmission is used with currently available standards simultaneously for different signal sources.
  • a specific signal source is selected according to the invention in the constellation diagram.
  • the selection is implemented on the basis of specific subcarriers and/or portions of a signal, for example, of an OFDM signal.
  • a signal for example, of an OFDM signal.
  • frequency-dependent disturbances of the transmission channel can be determined in this manner.
  • the selection is implemented on the basis of specific symbols of a transmission frame, for example, only of the preambles, only of the transmission-frame header or only of the transmission-frame end.
  • frame-dependent disturbances of the transmission channel can be determined in this manner.
  • a device for the graphic display of I/Q values of a baseband signal includes a selection unit configured to select a subset of I/Q values from a set of I/Q values of a baseband signal, wherein the non-selected I/Q values of the set form a non-selected subset.
  • the device further includes a calculation unit configured to calculate a frequency of occurrence of each I/Q value of the selected subset.
  • the device further includes an assignment unit configured to assign display information to each I/Q value of the selected subset, wherein the display information at least corresponds to the respective frequency of occurrence.
  • the device further includes a data buffer configured to store at least the selected subset of I/Q values, wherein the frequency of occurrence for each I/Q value of the selected subset is stored with the respective I/Q value.
  • the device further includes a display unit configured to display the set of I/Q values of the baseband signal in a constellation diagram, based at least in part on the display information, wherein the I/Q values of the non-selected subset is displayed in a different manner from the I/Q values of the selected subset. Accordingly, through the selection of a subset of I/Q values, the computational effort is considerably minimized, and the clear visual organization of the display is enhanced.
  • the I/Q values of the non-selected set provide an identical display information.
  • the display information provides a subset indicator, which, for example, comprises a 1-bit information that displays whether an I/Q value is a part of the selected subset or not. Accordingly, with this low technical effort for each I/Q value, it is easily possible to distinguish between a selected and a non-selected I/Q value. For example, the calculation unit and the assignment unit can be simply controlled in this manner.
  • the display information is a color information of the pixel representing the I/Q value.
  • the display information is a contrast information of the pixel of the display unit representing the I/Q value.
  • the display information of the selected subset is different from the display information of the non-selected set of I/Q values.
  • all I/Q values of the non-selected set are provided with an identical display information.
  • FIG. 1 illustrates a flow chart depicting a method for the display of constellation diagrams, in accordance with example embodiments of the present invention
  • FIG. 2 illustrates a constellation diagram with constellation points of different modulation types
  • FIG. 3 illustrates an enlargement of a specific constellation point (point 6 ) of the constellation diagram of FIG. 2 ;
  • FIG. 4 illustrates a constellation diagram with a selected subset of I/Q values, in accordance with example embodiments of the present invention
  • FIG. 5 illustrates a block diagram depicting an example device for the display of constellation diagrams, in accordance with example embodiments of the present invention.
  • FIG. 6 illustrates a block diagram depicting an alternative example device for the display of constellation diagrams, in accordance with example embodiments of the present invention.
  • FIG. 1 illustrates a flow chart depicting a method for the display of constellation diagrams, in accordance with example embodiments of the present invention.
  • a selection step 1 a subset of I/Q values of a baseband signal is selected.
  • a calculation of the frequency of occurrence 10 , 11 , 12 of the respective I/Q value is implemented on the basis of the selected subset of these I/Q values.
  • a display information is assigned to every selected I/Q value on the basis of the frequency of occurrence 10 , 11 , 12 .
  • the selected I/Q value with the display information is displayed on a display element in a constellation diagram 5 .
  • FIG. 2 illustrates a constellation diagram 5 , with constellation points of different modulation types, in accordance with example embodiments of the present invention.
  • the constellation diagram 5 shows a complex I/Q plane, wherein the real part of a complex symbol present in the baseband is displayed on the I axis, and the imaginary part of the complex symbol is displayed on the Q axis.
  • the complex symbols are entered corresponding to their modulation at the respective constellation point 6 of the constellation diagram 5 .
  • the constellation diagram 5 according to FIG. 2 comprises a baseband signal with complex symbols for three different modulation types.
  • a first modulation 7 is, for example, a 2 BPSK modulation.
  • the constellation points of this first modulation 7 are disposed on the axis of the constellation diagram 5 and are used especially for the transmission of pilot symbols, since only the phase of the complex symbols varies through +/ ⁇ 180°, and a high probability of detection and robustness of these constellation points is present.
  • a 4-QPSK is shown in the constellation diagram 5 according to FIG. 2 as a second modulation 8 , wherein QPSK is an abbreviation for Quadrature Phase Shift Keying. Accordingly, only one constellation point 6 of the second modulation 8 is arranged in every quadrant of the constellation diagram 5 , which also leads to a simple detectability of the constellation point and to a corresponding robustness in the signal path susceptible to interference.
  • the QPSK is thus characterized in that the amplitudes of the individual constellation points carry no information, since all of the symbols provide the same spacing distance relative to the zero point.
  • the constellation diagram 5 provides a third modulation 9 , for example, a 16-fold quadrature amplitude modulation, abbreviated as 16-QAM.
  • a third modulation 9 for example, a 16-fold quadrature amplitude modulation, abbreviated as 16-QAM.
  • 16-QAM quadrature amplitude modulation
  • four symbols are provided in each quadrant of the constellation diagram 5 , so that this third modulation is more susceptible to interference.
  • decision errors based on disturbances in the signal path can lead to incorrect assignments in the constellation diagram 5 .
  • a 4-QAM could be accommodated in the constellation diagram 5 as a fourth modulation.
  • the constellation points of the 4-QAM would then be identical to the constellation points of the modulation 8 , namely, the 4-QPSK.
  • a possibility for selection has been created according to the invention in order to distinguish the individual symbols of the 4-QAM from the signals of the 4-QPSK.
  • first symbols can be accommodated in the constellation diagram 5 with the 16-QAM as the third modulation 9 alongside second symbols of the 16-QAM as the third modulation 9 in the constellation diagram 5 .
  • a possibility for selection was created according to the invention in order to distinguish the first symbols from the second symbols of the 16-QAM.
  • FIG. 3 illustrates an enlargement of a specific constellation point (point 6 ) of the constellation diagram of FIG. 2 .
  • the signal status 00 of the 4-QPSK modulation 8 according to FIG. 2 has been enlarged in the display.
  • this constellation point 6 provides three different frequency-of-occurrence thresholds. Accordingly, a first frequency of occurrence of the I/Q value with reference number 10 is shown. A second frequency of occurrence of the I/Q value is presented with reference number 11 , and a third frequency of occurrence of an I/Q value is shown with reference number 12 .
  • the individual I/Q values are displayed as pixels on the display element 17 .
  • a calculation unit 15 calculates the frequency of occurrence with which an I/Q value occurs.
  • a counter may be used, for example, which determines the number of I/Q values occurring and increments a counter value whenever the I/Q value has again been detected another time.
  • a display information is assigned to every frequency of occurrence of an I/Q value.
  • a three-stage display information has proved particularly good with regard to visual perception. From a given threshold value, a corresponding display information is assigned to the I/Q value.
  • the display information can be a color information, a contrast value and/or a brightness value.
  • the display information can also be a texture information, a pattern information and/or hatching information.
  • I/Q values with a high frequency of occurrence 12 are displayed, for example, as red pixels.
  • I/Q values with a medium frequency of occurrence 11 are displayed, for example, as yellow pixels.
  • I/Q values with a low frequency of occurrence 10 are displayed, for example, as green pixels.
  • a three-stage threshold-value scale is selected for the frequency of occurrence in order to achieve the maximum possible visual significance with the assistance of a display information of only 2 bits in size.
  • the relative frequency of occurrence of the respective I/Q value is calculated, that is to say, the frequency of occurrence of the respective I/Q value relative to the total number of I/Q values of this constellation point in the constellation diagram 5 .
  • the number of frequency-of-occurrence thresholds is not restricting.
  • only one threshold is provided in order to separate the I/Q values of the selected subgroup from the I/Q values of the non-selected subgroup.
  • the frequency of occurrence is displayed in a multi-stage manner, for example, 10-stage or 15-stage.
  • the frequency of occurrence is displayed by means of a continuous color-characteristic scale.
  • the value of the frequency of occurrence counter could be used directly in this manner.
  • FIG. 4 illustrates a constellation diagram with a selected subset ( 13 ) of I/Q values, in accordance with example embodiments of the present invention.
  • the second modulation 8 has been displayed as a selected subset 13 of I/Q values with a distribution of frequencies of occurrence.
  • the other constellation points 6 of the constellation diagram 5 are presented in a uniform display, wherein, for example, a uniform grey tone or a uniform contrast setting should be selected. Accordingly, the user of the constellation diagram 5 is offered a simple possibility for displaying in color only those I/Q values which are relevant for an error analysis, starting from an abundance of I/Q values.
  • the dashed lines in FIG. 4 show that the selected constellation points 6 of the subset 13 can also include non-selected I/Q values, especially with the use of different symbols on the same constellation point 6 and a selection of only one of the different symbols.
  • a 4-QAM could also be displayed with a 4-QPSK together in a constellation diagram 5 , wherein the I/Q values of the 4-QAM or the 4-QPSK can be displayed separated from one another through an appropriate selection.
  • FIG. 5 illustrates a block diagram depicting an example device for the display of constellation diagrams, in accordance with example embodiments of the present invention.
  • a demodulation unit 14 provides a quadrature modulator typical for I/Q-based baseband signals, wherein an intermediate frequency IF is multiplied using two carrier waves displaced by 90°.
  • a cos( ⁇ t) carrier frequency is used to obtain the IN-phase component of the I/Q value 6 .
  • a ⁇ sin( ⁇ t) carrier frequency is used to obtain the QUADRATURE-phase component of the I/Q value 6 .
  • the resulting in-phase and quadrature-phase components of a constellation point 6 are now presented to a calculation unit 15 corresponding to their modulation 7 , 8 , 9 .
  • the calculation unit 15 which I/Q values should be displayed with a frequency of occurrence 10 , 11 , 12 .
  • a selection unit 16 is provided.
  • the calculation unit 15 presents the selected and the non-selected I/Q values to a display 17 , wherein the selected I/Q values are displayed with a display information not equal to the display information of the non-selected I/Q values of the display 17 .
  • the selection is implemented on the basis of a transmission frame of the signal, so that, a selection is made, for example, between the preamble frame, the data frame, the frame end or the frame header, in order to provide a statement regarding the susceptibility of different frames to interference in the transmission.
  • the selection is made on the basis of specific subcarriers in order to investigate, especially, the frequency dependence of broadband signals.
  • FIG. 6 illustrates a block diagram depicting an alternative example device for the display of constellation diagrams, in accordance with example embodiments of the present invention.
  • the modulation 7 , 8 , 9 is not used as the selection criterion here, but one of the three different signal sources.
  • a selection unit 16 which is controlled, for example, by the user, selects the signal source 2 as the signal source of which the I/Q values are to be displayed with a frequency of occurrence 10 , 11 , 12 .
  • the associated I/Q values according to signal source 2 are calculated by means of an assignment unit 18 corresponding to their frequencies of occurrence 10 , 11 , 12 .
  • display information are assigned to the respective I/Q value.
  • the assigned display information is based upon a previously calculated frequency of occurrence 10 , 11 , 12 .
  • the I/Q value is stored with the display information in a data buffer 19 . Accordingly, the I/Q value itself with the respective display information is stored in the data buffer 19 .
  • the I/Q values of the signal sources 1 and 3 are rerouted to the display unit (Display) 17 with the display information provided according to signal source 2 .
  • the display unit 17 displays a pixel corresponding to the I/Q values which are stored in the buffer 19 with the display information linked to them. Accordingly, an associated address in the buffer 19 is read out for a pixel of the display unit 17 .
  • the address in the buffer 19 then comprises the I/Q value and the associated display information.
  • the display can be time-limited, wherein a counter status associated with the pixel address is incremented within a predetermined time span, in each case whenever a further I/Q value has been determined for this address via the calculation unit 15 , and accordingly a respective pixel has been determined on the display element 17 . In this manner, the frequency of occurrence with which this address and the associated pixels occur is stored under every address of the data buffer 19 .
  • the display information is assigned to the frequency of occurrence by means of an assignment unit 18 .
  • 3 bits are used for each pixel.
  • a first bit is used as the subset indicator in order to show that the I/Q value belongs to a selected subset 13 .
  • the two further bits contain the display information, especially a color tone based upon the three-stage threshold value.
  • the I/Q value is displayed on the basis of three colors. The three colors can be adjusted by the user. The default setting of the colors is selected in such a manner that the rare values are visually emphasized, that is, that a strong contrast for these I/Q values is given.
  • the respective constellation points 6 can also be frozen, wherein the constellation diagram 5 is not updated from the time of the so-called freeze setting. However, the calculation of the I/Q values is continued in the background. This freezing can be adjusted via an operating button of the device.
  • constellation points 6 used in a multiple manner and different signal sources can serve as a basis for an I/Q value in many broadcast standards (radio standards), a selection is made according to the invention in order to allow an error analysis. This means that only selected subcarriers or symbol types appear in the color of the frequency of occurrence, while all non-selected I/Q values are displayed without intensity distribution.

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  • Electromagnetism (AREA)
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  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
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DE102013216300.2A DE102013216300B4 (de) 2013-08-16 2013-08-16 Verfahren und Vorrichtung zum grafischen Darstellen von I/Q-Werten eines Basisbandsignals
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Citations (4)

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DE19547896A1 (de) 1995-12-21 1997-07-03 Rohde & Schwarz Anordnung zum Darstellen der Signalzustände eines QAM-modulierten Signals
DE10161602A1 (de) 2001-12-14 2003-06-18 Rohde & Schwarz Verfahren und Anordnung zum graphischen Darstellen der l- und/oder Q-Komponenten von digital modulierten Hochfrequenzsignalen
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US5539772A (en) * 1994-10-13 1996-07-23 Westinghouse Electric Corporation Apparatus and method for verifying performance of RF receiver
DE19547896A1 (de) 1995-12-21 1997-07-03 Rohde & Schwarz Anordnung zum Darstellen der Signalzustände eines QAM-modulierten Signals
US6417834B1 (en) 1995-12-21 2002-07-09 Rohde & Schwarz Gmbh & Co. Kh Arrangement for displaying the signal statuses of a QAM-modulated signal
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DE10161602A1 (de) 2001-12-14 2003-06-18 Rohde & Schwarz Verfahren und Anordnung zum graphischen Darstellen der l- und/oder Q-Komponenten von digital modulierten Hochfrequenzsignalen
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Schenk, "Grobkarolinefeld-High Frequency Test Equipment", Kriebel-Tour 2010, KWS-Electronic GmbH, 2010.

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